This invention relates generally to apparatus for heat treating workpieces and, more particularly, to a rotary retort heat treating furnace. In such a furnace, loose workpieces are loaded into a drum-like retort mounted to rotate about a horizontal axis and adapted to be heated to high temperatures. As the retort is rotated, means such as a helical flight within the retort advance the workpieces gradually through the retort while causing the workpieces to tumble continuously during their advance so as to fully expose all portions of the workpieces to heat and to a treating gas. The workpieces usually are discharged from the retort into a quench tank of oil or water.
Most commercially available heat treating retorts are heated by gas-fired burners. Heat is generated at the outer surface of the retort and then is transferred by conduction through the retort wall to the workpieces. In order to promote efficient thermal conduction and to reduce thermal stress in the retort, it is necessary to make the retort of relatively thin-walled construction in an effort to decrease the temperature gradient between the inner and outer sides of the retort. By virtue of its thin-walled construction, a retort of any substantial length tends to sag and flex severely under the weight of the tumbling workpieces and ultimately will fail as a result of fatigue. Because of the limitations on the practical length of the retort, it is necessary to make the retort comparatively large in diameter in order to enable the retort to achieve an adequate production rate.